Handle VCSs; skip missing ocamlformat; append existing files

[toastal]

Missing: tests. I do not know how to write these.

Tests that would be nice to have:

1. .ocamlformat is missing if the binary is missing; there is already a warning, so I don’t think a blank file needs to be echoed… especially since there exists alternative formatters
2. echo "# Hello, world! > .gitignore", & test that that string is still there since _build/ should be appended.

Appending is required to support Pijul since pijul init creates .ignore with .git & .DS_Store by default.

[toastal]

bump?

[maxRN]

Hey @toastal I think you should open the PR against the actual dune repository or it won't show up and can easily get lost. (Seems like this PR went under the dune maintainers' radar)
If you are no longer interested in this change I would also be more than happy to take this on and see this change through.

[toastal]

Oh I am still very much in favor of this using topiary for formatting & Darcs or Pijul for VCS & do not wish to see hegemonic endorsement when multiple options can/should be easily supported. I was pretty vocal in the upstream commits since it now gives me extra steps of stuff I need to remove, so I made these patches to cover myself while still aiming for the initial good intent of this commit to have some defaults. I would assume someone would see those patches, but I am unsure what you mean about a pull request upstream when this hasn’t been merged.

[maxRN]

Ah, sorry for the confusion. I was reading ocaml#9567 and didn't notice that you had created a PR against the dune Repo already. I read until the bottom and this is where I found the link to this PR. I see that you commented on the PR again to bump it, hopefully that means it will pick up steam again. Very happy to see this feature being worked on.